Insulated electrical conductor



Feb. 20, 1945. J. J.' KEYES l 2,370,045

INSULATED ELECTRICAL CONDUCTOR Filed March 20, 1942 Vif, l

6705; /r/bews WITNESSES: INVENTOR M y JO?? J eyes.

l messed Feb. zo, 194s INSULATED ELECTRICAL CONDUUIOB John J. Keyes, Edgewood, Pa., signor to Westinghouse Electric Manufacturing Company, East Pittsburgh, Pa., a corporatimrof` Pennsylvania Application March 20, 1942, Serial No..435,445

13 Claims. (Cl. 174-120) This invention relates to electrical conductors carrying electrical insulation. More particularly, the electrical insulation comprises glass fibers and a resinous composition applied thereto to provide for a smooth, highly insulative and impregnated coating on the conductor.

The object of this invention is to provide for applying to glass fibers upon conductors a binder cooperative therewith to produce a smooth-surfaced, tightly adherent insulation having good electrical properties.

A further object of this invention is to provide for applying glass fibers in the form of sliver in combination with a binder to produce a smoothsurfaced, tightly adherent, insulating coating upon electrical conductors.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the single figure of the drawing illustrating an electrical conductor embodying the novel features of the invention.

It has been proposed heretofore to apply glass fibers to electrical conductors to produce insulation capable of operating at temperatures substantially above those at which insulated conductors maybe operated at the present time. Since insulation composed only of glass fibers consists of non-porous glass drawn into various lengths with interstices therebetween, the effectiveness of the glass fibers as insulation is determined by the nature of the material in the interstices between the fibers. If better than air insulation is required, it is necessary to impregnate the interstices between the glass fibers with an insulative material.

It has been suggested to use glass fibers in combination with various resinous materials in order to produce a combined electrical insulation having desirable electrical properties. Due to the cost of spun glass fibers, it has been desirable to apply as thin a combination of the glass fibers and resinous impregnating material as possible.

Glass fibers are sold to the trade in two main forms suitable for applying to electrical conductors. Continuous fibers prepared from continuous laments of spun glass of a diameter of less than 0.002 inch have been used almost exclusively for coating electrical conductors, particularly in the standard magnet wire sizes. One or more thicknesses of the spun glass bers can be wrapped closely together about the electrical conductor to produce a relatively thin and smooth insulation. 'll'lieY second commercially 5 available form of glass fibers is sliver. In sliver the glass bers consist of small lengths of the order of from one inch to eighteen inches combined into a loose mass. When glass flbers in the form of sliver have been applied to lelectrical conductors, it was discovered that thin layers having a smooth surface have been substantially impossible to produce. The numerous short lengths of glass bers protrude when the sliver has been applied to the conductor to produce a fuzzy or woolly surface body. When resin is applied to this material in order to impregnate it, the final cured product is exceedingly rough with numerous projecting glass fibers present on the surface. This is a relatively dusty material since the projecting bers break off. The handling of the material causes itching. Tight coils, for example, cannot be produced from this type of material. Therefore, space eiliciency would have to be greatly reduced ii' glass of the type of sliver were employed upon conductors. On bending the conductors. it was found that the turns of sliver separated readily to expose the bare conductor. Accordingly, the art has been limited to a great extent to the use of the glass fibers in the form of continuous filaments.

In some cases sliver composed of staple iibers is drawn and twisted into what is designated in the art as "staple yarn. Such staple yarn is a tighter twisted product than sliver, but when applied to conductors under prior art practice, it results in the same objectionable roughness and loose, protruding bers. The present invention contemplates the treatment of staple yarn to produce a satisfactorily smooth and uniform insulation on conductors. i

Since synthetic glass bers consisting of continuous filaments are approximately three times as expensive per pound as compared to the glass fibers in the form of sliver, it is desirable to employ glass sliver for economical reasons. Due to these factors of rough surface and projecting fibers, it has been substantially impractical to employ the glass sliver, in spite of the difference in prices of the material. Burnishing dies and similar apparatus have been relatively ineffective in producing satisfactory surface coatings lof glass sliver on conductors.

According to this invention, it has been discovered that certain resinous compositions or combinations of resinous compositions may be applied to glass fibers in the form of sliver to give a product that is so much smoother than the results obtained heretofore with glass sliver that the materialA may be applied for the same apdrawing which is a schematic view of the conductor in various stages gf Vapplication of the insulation. The conductor VI2 'is preferably initially coated with a layer of the resinous composition I4 either of the type disclosed in the Examples Nos. 1 and 2, or, in some cases, polyvinyl alcohol alone or any other resinous material capable of adhering to the glass fibers and to the conductor may be applied. The polyvinyl alcohol suitable for the resinous layer I4 may consist of from a 5% to 15% solution of polyvinyl alcohol derived from a polyvinyl ester hydrolyzed to such an extent that it is soluble in a water-alcohol solution. The water-alcohol solution is employed as a carrier or solvent for thepolyvinyl alcohol. The glass fibers in the form of sliver i6 are wrapped about the conductor upon the wet or tacky resin coating il. One or more layers of sliver may be superimposed. Suitable spinning y heads for so applying the glass sliver are well known in the art and need not be described here. A layer of glass ilbers Il with numerous projections and having a woolly or fuzzy appearance is produced at this stage since no impregnant has been applied upon the glass fibers.

One of several procedures for applying an impregnating and binding resin to the glass fiber coating I8 may be followed to produce a satisfactory final product. The following procedurehas been particularly satisfactoryv for the purpose of the invention: l

Tnnrusn'r No. 1

The resinous composition solution of either Example No. 1 or Example No. 2 containing polyvinyl alcohol is applied, for example, by clipping or pumping onto the wire to the glass fiber layer I8 and baked in standard enameling towers for a fraction of a minute at temperatures of from 300 C. to 600 C. The baking removes the liquid TREATMENT No. 2

The glass coating Il may be satisfactorily treated by applyingpolyvinyl alcohol solution carrier present and cures the resin. While a' fairly smooth coating is produced by application of this resin alone, it has been discovered that a subsequent application of polyvinyl alcohol alone produces a somewhat improved product with a much smoother vsurface with no projections of glass fibers. A 5% polyvinyl alcohol solution in water and ethyl alcohol as the solvent is applied to the conductor and baked at about the same conditions as the composite resinous composition. The conductor will now present an exceedingly smooth surface 20 which is capable of being wound into tight coils or put in motor or generator slots with ease. Substantially no projections of glass fibers will be evident on the surface. The effect is similar to that produced by passing other fibrous materials through burnishng dies. In some cases, in order to insure a more complete application of impregnating material to the glass coating I8, a second application of the phenol-formaldehyde-oil modified alkyd resin having a small amount of polyvinyl alcohol may be made. After baking, the conductor may be again coated with polyvinyl alcohol alone followed by a final baking to effect a cure. The final product produced after applying the four coatings applied to the glass sliver is an exceedlngly desirable form of electrical insulation.I

Since the resinous composition applied to the glass nbers has approximately solids and even higher, the fill is greatly superior to that produced by other synthetic resins having much lower proportions of solvents. For example, polyvinylal resins have the undesirable characteristic of forming extremely viscous solutions at initially followed by baking to remove the liquid carrier and a subsequent coating of the composition of phenol-formaldehyde, oil-modified alkyd resin and polyvinyl alcohol. Baking after this treatment will produce a conductor that is satisfactory for use, or in some cases, an external coating of polyvinyl alcohol solution followed by a ilnal bake will produce a highly insulated conductor.

TnnA'rMnNr No. 3

lln some cases, where the resinous solution of phenol formaldehyde and oil-modified alkyd resin contains a relatively large amount of polyvinyl alcohol, two or three successive applications thereof, without applying any polyvinyl alcohol alone, have produced insulation carrying glass fibers in the form of sliver which is satisfactory for the purposes of the invention.

Ordinarily the initial resin application I4 on the conductor is desirable. In some cases it may be dispensed with providing the subsequently applied sliver is thoroughly impregnated down to the conductor to e'ect adequate bonding.

It will be appreciated that the advantages of the invention are most pronounced when the cheapest commercial form of glass fibers, namely, sliver, is employed in cooperation with the resin. However, the advantages of the resin are so pronounced that, in some cases, it will lend itself to use with other forms of glass fibers, since it effects a good bond between the glass and the conductor as Well as being a good impregnant for the interstices between glass fibers. It is of value when used in combination with staple yarn or with continuous filaments.L Glass fibers which may be applied in felted form to conductors may be satisfactorily treated by means of the compositions and the Selected arrangement of coatings herein disclosed.

It will be apparent that the resinous composition and polyvinyl alcohol alone may be applied as successive coatings to the glass sliver once or in a plurality of successive coatings.

The flexible unitary insulating material produced in the manner set forth `above may be applied to electricalv conductorsA having either a stranded core or formed of solid wire.

Since certain changes in carrying out the above process, and certain modifications in the article which embody Vthe invention may be made without departing from its scope, it is intended that all matter contained in the above description or shown in the drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. An insulated conductor comprising, in combination, an electrical conductor, glass fibers in the form of sliver wrapped about 'the conductor, and a resinous composition applied to the electrical conductor and heat treated to closely bind the glass sliver thereto, the composition impregnating the interstices between the glass bers to provide for a, smoothA exterior surface free v bination, an electrical conductor, glass bers in i the form of sliver wrapped about the conductor, and a resinous composition applied to the electrical conductor and heat treated to closely bind the glass sliver thereto, the composition impregnating the interstices between the glass fibers to provide for a smooth exterior surface free from. projecting glass fibers and toprovide for good electrical insulation, the resinous composition applied as a plurality of coatings, including an inltial coating upon the conductor composed of phenol formaldehyde combined with an oil-modified alkyd resin, subsequent coatings applied to the sliver composed of phenol-formaldehyde combined with an oil-modied alkyd resin and a hydrolyzed polyvinyl ester and coatings of the hydrolyzed polyvinyl ester alone.

3. An insulated conductor comprising. in combination, an electrical conductor, glass fibers in the form of sliver wrapped about the conductor, and a resinous composition applied to the electrical conductor and heat treated to closely bind electrical insulation, the resinous composition ap- I..

plied as a plurality of coatings, including an initial coating upon the conductor composed of from 10 to 25 parts of phenol-formaldehyde com'- bined with from 25 to 100 parts of an oil-modified alkyd resin, subsequent coatings applied to the sliver composed of from 10 to 25 parts of phenolformaldehyde combined with from 25 to 100 parts of an oil-modified alkyd resin and 2 to 20 parts of hydrolyzed polyvinyl ester and coatings of the hydrolyzed polyvinyl ester alone.

4. An insulated conductor comprising, in combination, an electrical conductor, glass bers in the form of sliver wrapped about the conductor, and a resinous composition applied to the conductor and the sliver and heat treated to closely bind the glass sliver to the conductor, the composition impregnating the interstices between the 6. In the method of applying glass fibers in the form of sliver in combination with aresinous binder and impregnant for the interstices between glass nbers to an electrical conductor to provide for electrically insulating the conductor comprising, applying a sliver of glass fibers to the electrical conductor, applying a hydrolyzed polyvinyl ester in a liquid carrier to the applied sliver, heat-treating the conductor to remove the liquid carrier, applying a resinous compositionv composed of phenol-aldehyde, an oil-modiiled alkyd resin and a hydrolyzed polyvinyl ester in a liquid medium, and heat-treating the conductor to remove the liquid medium and to cure tbe applied materials to produce aninsulated conductor.

glass bers to provide for a smooth exterior surface relatively free from projecting fibers and to provide for good electrical insulation, the resinous composition composed of a substantially phenol-free phenol-formaldehyde, the reaction product of a dibasic acid, a polyhydric alcohol and an oil, and a hydrolyzed polyvinyl ester.

5. Aninsulated conductor comprising, in combination, an electrical conductor, glass bers in the form of sliver wrapped about the conductor, and a. resinous composition applied to the conductor and the sliver and heat treated to closely bind the glass sliver to the conductor, the composition impregnating the interstices between the glass bers to provide for a smooth exterior surface relatively free from projecting fibers and to provide for good electrical insulation, the resinous composition composed of from l0 to 25 parts of a substantially phenol-free, phenolformaldehyde, from 25 to 100 parts of the reaction product of a dibasic acid, a polyhydrlc alcohol and an oil, and from 2 to 20 parts of hydrolyzed polyvinyl ester.

'7. In the method of applying glass bers in the form of sliver in combination with a resinous binder and impregnant for the interstices between glass nbers to an electrical conductor to provide for electrically insulating the conductor comprising, applying` to the electrical conductor a resinous binder capable of adhering to glass ilbers, applying a sliver of glass bers to the electrical conductor upon the resinous binder, applying ahydrolyzed polyvinyl ester in a. liquid carrier to ,theA applied sliver, heat-treating the conductor to remove the liquid carrier, applying a resinous composition composed of phenol-aldehyde, an oil-modified alkyd resin and a hydrolyzed polyvinyl ester in a liquid medium, and heat-treating the conductor to remove the liquid medium and to cure the applied materials to produce an insulated conductor.

8. In the method of applying glass fibers in the form of sliver in combination with a resinous binder and impregnant for the interstices between glass bers to an electrical conductor to provide for electrically insulating the conductor comprising, applying a sliver 'of'glass fibers to the A g electrical conductor, applyinga hydrolyzed polyvinyl ester in a liquid carrier to the applied sliver, heat-treating the conductor to remove the liquid carrier, applying a resinous composition composed of phenol-aldehyde, an oil modified alkyd resin and a hydrolyzed polyvinyl ester in a liquid medium, and heat-treating the conductor to remove the liquid medium and to cure the applied material, applyin'g a coating of hydrolyzed polyvinyl ester in a liquid carrier to the conductor and heat-treating the conductor to remove the solvent and to render the applied coating adherent, to the glass bers to produce a smoothsurfaced insulated conductor.

9. The method of applying glass ilbers in the form' of sliver in combination with a resinous binder and impregnant for the interstices between glass fibers to an electrical conductor to provide for electrically insulating the conductor comprising, applying to the electrical conductor a resinous binder capable of adhering to glass bers, applying a sliver of glass fibers to the electrical conductor, applying a, first coating of a resinous composition composed of phenol-aldehyde, an cil-modied alkyd resin and a hydrolyzed polyvinyl ester, lheat-treating the coating, applying a hydrolyzed polyvinyl ester in a liquid carrier to the applied sliver, heat-treating the conductor to remove the liquid carrier, applying a second coating of resinous composition composed of phenol-aldehyde, an oil-modied alkyd resin and a hydrolyzed polyvinyl ester in a liquid medium, and heat-treating the conductor to remove the liquid medium and to cure the appliedV material, applying a coating oi hydrolyzed polyvinyl ester in a liquid carrier to the conductor and heat-treating the conductor to remove the solvent and to render the applied coating adherent to the glass bers to produce a sn'ioothsurfaced insulated conductor.

10. The method of applying glass iibers in the to the conductor and heat-treating the conductor to remove the solvent and to render the applied coating adherent to the glass fibers to produce a smooth-surfaced insulated conductor.

1l. An insulated conductor comprising, in combination, an electrical conductor, glass iibers se lected from the class consisting of sliver and staple yarn applied to the conductor, and a resinous composition applied to the electrical con'- ductor and heat treated to bind the glass sliver thereto, the composition impregnating the interstices between the glass bers to provide for a smooth exterior surface free from projecting glass bers and to provide for good electrical insulation, the resinous composition composed of an oil-modied alkyd resin, phenol-formaldehyde and hydrolyzed polyvinyl ester.

12. An insulated conductor comprising, in combination, an electrical conductor, glass fibers se- 'form of sliver in combination with a resinous l lected from the class consisting of sliver and staple yarnvapplied to the conductor, and a resinous composition applied to the electrical conductor and heat treated to closely bind the glass libres thereto, the composition impregnating the interstices between the glass bers to provide for a smooth exterior surface free from projecting glass fibers and to provide for good electrical insulation, the resinous composition applied as a plurality of coatings, including an initial coating upon the conductor' composed of from l0 to 25 parts of phenol-formaldehyde combined with from 25 to 100 parts of an oil-modied alkyd resin, subsequent coatings applied to the sliver composed of from 10 to 25 parts of phenol-formaldehyde combined with from 25 to 100 parts of an oil-modified alkyd resin and 2 to 20 parts of hydrolyzed polyvinyl ester and coatings of the hydrolyzed polyvinyl ester alone.

13. An insulated conductor comprising, in combination, a conducting member, glass bers in the form of sliver or yarn applied to the conducting member, and a resinous composition applied to bond the glass sliver to the conducting member, the resinous composition impregnating the interstices between the fibers of the glass sliver to pro,

vide a smooth exterior surface free from projecting ends of glass bers and good electrical insulation, the resinous composition applied as a plurality of coatings, including at least one coating composed of phenol-formaldehyde combined with an oil-modified alkyd resin, and at least one coating of a hydrolyzed polyvinyl ester applied to the glass fibers whereby the glass fibers are drawn in and closely bound to the conductor.

` JOHN J. KEYES. 

